Shotgun cartridge obturator, method for preparing a cartridge equipped with said obturator and equipped cartridge

ABSTRACT

The invention relates to a shotgun cartridge comprising a case (12) of internal diameter dINT and a base (14) with a primer (16), the powder (18), a wad (22) and the shot (24), as well as an obturator (20) arranged between the powder (18) and the wad (22), characterized in that the obturator (20) is made of biodegradable material with plastic deformation properties, and comprises a central disk (25) and ribs (26) together forming a one-piece element with the disk, the assembly having an outer diameter dEXT, the ribs (26) comprising upper ribs (27) and lower ribs (28), these ribs (26) forming a non-zero angle with the plane of the disk (25), the obturator having a nominal outer diameter dEXT, the ribs being able to take at least one other position in which said ribs (26) are in the plane of the disk (25), the outer diameter being DEXT. The invention also concerns a method for producing a shotgun cartridge.

The present invention relates to a shotgun cartridge obturator and a method for preparing a cartridge equipped with said obturator. The invention also relates to the equipped cartridge of said obturator.

In the field of shooting for hunting and sporting purposes, a large number of cartridges are used. A cartridge usually comprises a primer, a powder charge, one or more wad-type accessories to transfer the power generated by the explosion of the charge to the projectiles and/or a basket intended to contain said projectiles during the transfer phase.

There are very many architectures and types of accessories. Similarly, the material of the projectiles may be lead or steel and in all cases different problems must be overcome.

All the elements are contained in an envelope comprising a base which is usually made of metal and a body which is usually made of card, both materials being recyclable.

A common and basic problem with cartridges is transferring the power generated by the explosion of the charge to the pellets while limiting power losses as much as possible.

Moreover, environmental awareness is leading users and manufacturers to turn to cartridges with no oil-based plastics materials. Biodegradable materials exist and so it seems natural to utilize these materials. A first technical problem posed when using a biodegradable replacement material is that by definition biodegradable materials have a shorter lifespan than oil-based plastics materials, their mechanical properties do not equal those of plastics materials and those same mechanical properties deteriorate faster than those of plastics materials.

A second problem is linked to the fact that because their mechanical properties are inferior and subject to change, biodegradable materials often fall apart under the stresses instead of remaining in one piece.

Different assemblies and arrangements exist but a sporting or hunting cartridge arrangement is described here, having the following elements listed from bottom to top for a cartridge placed vertically:

-   -   a metal base containing the primer and the powder on which an         obturator or over-powder card is placed,     -   a tube forming the case of the cartridge, rigidly connected to         the base, receiving a wad placed above the powder, and shot of         different types, of a chosen diameter, arranged above said wad,     -   a crimping of the tube forming the case of the cartridge at the         end thereof, in the region of the upper surface of the shot, to         close and compress the assembly of elements contained therein.

Over-powder cards do not give good performance and are generally replaced by an obturator made of a plastics material.

When the cartridge is fired, the primer is struck, the powder ignited by the primer burns instantaneously and this combustion produces a large volume of gas. The explosion results from said gases being confined in the barrel of the weapon. It is when subject to the thrust of the gases generated that the elements, projectiles and accessories introduced into the sleeve formed by the base and the case thereof, are expelled from the weapon through the cylinder of the FC barrel.

The projectile, usually shot, is thus expelled by transmitting the energy generated by the explosion. The energy due to the thrust of the gases is transmitted first through the obturator which prevents the power of the explosion applied directly to the wad from being lost. But for optimized ballistic performance the obturator, as the name indicates, must be as airtight as possible in order to confine said gases and transfer the power of the gases to the wad and then to the projectile.

The seal between the inner wall of the case and the peripheral edge of the obturator must be airtight. The energy of the explosion is then transmitted to the shot through the wad so as to ensure equal distribution of the energy while minimizing losses.

The role played by said obturator is paramount in firing quality and shot projection. This is because the obturator, by the intermediate positioning thereof between the explosion and the shot, acts as a gasket, which captures and channels the gases in order to transmit the energy of the explosion to the shot. It is important to control gas leakages in order to manufacture reliably consistent cartridges. This is even more complex as performance must be maintained over time and materials, particularly biodegradable materials, change.

An obturator of the prior art is described in U.S. Pat. No. 3,022,734. Said obturator is made of an oil-based thermoplastic elastomer, in particular polyethylene, styrene butadiene copolymer, or cellulose acetate. The method of manufacturing said obturator consists of cutting a blank ring with an extruded profile of circular cross section then deforming the disk between the dies of a punch to produce a profile with a substantially H-shaped cross section.

Because of the residual stresses, after deformation, the arms of the H naturally come to form a dish shape owing to the elastomer material.

The obturator is placed above the powder. The problem is that said obturator is made of an elastomer material with some flexibility, allowing deformation. Said obturator acts as a wiper seal and the edges deform randomly when subjected to thrust from the gases. Thus in the trade jargon this type of obturator “crumples,” in other words deforms randomly, and therefore the obturator must not only have a strong seal but uniform thrust must also be applied thereto.

Another obturator of a known type has an architecture that is stiffened in the central portion by ridges in the plane but is suitable for deforming radially by means of vertical lips. Said vertical lips are connected to the central portion by shoulders. At the moment of the explosion, the lip of the obturator is forcefully inflated to a pressure of at least 500 bar, possibly reaching 1000 bar in some loadings.

Nowadays even when ageing obturators made of a plastics material resist these considerable expansion stresses at both very hot and negative temperatures. But the profile of said obturators does not give satisfaction when made of biodegradable materials, which have poor resistance to said expansion stresses which gets even worse over time as said materials change. Moreover, as they become brittle when ageing, breaks may appear perpendicular to the shoulders causing leakages and a loss of ballistic power at the moment of the explosion. The environment too is an increasingly current concern, especially in sports practiced in the outdoors. In addition, cartridge producers want to make consumables that are more eco-responsible and have attractive biodegradability characteristics.

Biodegradable materials are becoming more highly developed but are still subject to changes in performance linked to the biodegradable composition.

Although said very slight biodegradability is imperceptible and of no importance for some elements, such as covers or other accessories, it can significantly affect the mechanical performance of a part such as an obturator for which the mechanical characteristics are fundamental.

The present invention proposes an obturator that may be made of a biodegradable material with plastic deformation properties that has a geometry that allows any biodegradation of the obturator over time to be compensated, further improving the airtight seal when thrust is generated by the explosion of the powder.

The present invention is now described in accordance with a non-limiting main embodiment, with reference to the accompanying drawings in which the different figures show:

FIG. 1: a front view of a cartridge with an obturator of the prior art,

FIG. 2: a front view of a cartridge with the obturator according to the present invention,

FIG. 3: a view from above of the obturator according to the present invention,

FIG. 4: a front view of the obturator according to the present invention,

FIG. 5: a front view of the obturator deformed by the compression generated by the explosion of the powder in the cartridge showing the dimensional variations,

FIGS. 6A and 6B: a view from above of the obturator in the case, a dotted line indicating the obturator immediately after the explosion of the charge,

FIG. 7A to 7D: a synoptic diagram of the method for producing and using a cartridge with the obturator according to the present invention.

FIGS. 1 and 2 describe a cartridge 10 comprising a case 12 and a base 14 equipped with a primer 16. The interior of the cartridge 10 contains the powder 18 placed in the region of the base 14 on which an obturator O and 20 is placed, the obturator O being an obturator of the prior art and the obturator 20 being the obturator according to the present invention. Each of the obturators O, 20 receives on top a wad 22, above which the shot 24, more generally the projectiles, is placed, in a known manner. The wad may be cup-shaped to better receive the shot.

The obturator 20 according to the present invention is shown in FIGS. 2 to 6, being shown deformed in FIGS. 5 and 6.

The obturator 20 comprises a central disk 25 with a thickness E and a diameter D, and has a lower face 20-1 and an upper face 20-2, lower and upper being considered with the cartridge placed vertically on its base.

The obturator 20 according to the present invention is manufactured in a single piece, the central disk having at least two upper ribs and at least two lower ribs 26, in this case eight upper ribs 27 and eight lower ribs 28, with which said central disk forms a one-piece element. The ribs 26 may resemble the petals of a daisy.

On the obturator 20, the upper ribs 27 and the lower ribs 28 number eight upper ribs 27 and eight lower ribs 28 respectively and spread outwards from the edge of the disk 25. Each of the upper 27 and lower 28 ribs comprise two radial rectilinear edges 30 and a circular outer peripheral edge 32, all the peripheral edges forming the periphery of the obturator 20 and thus an upper circular peripheral edge 34 and a lower circular peripheral edge 36. In the embodiment shown, each rib has a constant thickness e, said thickness e being less than E. The thickness E of the disk is less than or equal to twice the thickness e.

As can be seen in FIGS. 4 and 5, the angle of the ribs 26 relative to the plane of the central disk 25 is non-zero, viewed from the peripheral edge of the disk at the peripheral edge of the ribs. Looking at the disk 25 horizontally, the upper ribs 27 form an angle of more than 0° with the plane of the central disk 25. The lower ribs 28 form, symmetrically, an angle of less than 0°, also with the plane of the central disk 25. The angle varies depending on the caliber of the weapon and thus the diameter of the cartridge case, on the nature of the material, on the design of the cartridge and therefore on the wad or wads, and on the nature of the biodegradable material. Generally, the obturator gives complete satisfaction with any angle but tests will allow a person skilled in the art to quickly determine the optimum angle under routine working. The angle is more particularly between 20° and 40°.

Thus, the obturator comprises a central disk 25 and ribs 26 together forming a single-piece element, each rib 26 forming a non-zero angle with the plane of said disk 25.

The upper ribs 27 and the lower ribs 28 may or may not be connected by the radial rectilinear edges 30 thereof; in the present description said ribs are connected by a linking membrane 38. Because of its narrowness, said linking membrane 38 appears as a line. Said linking membrane 38 is placed between the ribs 26 and provides a preferably flexible connection between each of the upper ribs 27 and between each of the lower ribs 28, in particular to prevent deformation of the ribs during handling. Said linking membranes 38 have very little mechanical strength compared to the pressures and stresses that will later be involved when in use. In the plane of the disk 25, the upper ribs 27 are staggered relative to the lower ribs 28 such that the radial rectilinear edges of the lower ribs are angularly offset from the radial rectilinear edges of the upper ribs. Thus, and since the upper 27 and lower 28 ribs have the same geometry, the linking membranes 38 are not aligned along the longitudinal vertical axis. As can be seen in FIG. 3, the linking membranes 38 of the upper ribs 27 are advantageously positioned at the midpoint of the lower ribs 28 and vice versa, in order to maintain symmetry.

A deformable material with no resilient property is used for the obturator, which material is identical for the object in its entirety. The “no resilient property” characteristic refers to a material that is deformable but does not immediately recover its initial form once deformed. It is therefore a material of which the properties are referred to as “plastic,” not “resilient.” Thus if the ribs 26 are flattened, under stress, said ribs do not instantaneously return to the initial position when the stress ceases although a shape memory may be present.

From the point of view of geometry, the outer diameter d_(EXT) of the obturator is smaller than the inner diameter d_(INT) of the case in which said obturator is to be introduced. The diameter d_(EXT) is the theoretical diameter of the obturator in the operating position with the ribs in the plane of the disk 25.

The present invention proposes an obturator geometry that allows a biodegradable material with plasticity properties to be used.

The method for producing a cartridge equipped with the obturator according to the present invention consists of the following successive steps:

-   -   preparing a base with the case thereof, said base comprising a         primer and a powder charge,     -   introducing an obturator according to the present invention into         the case,     -   introducing at least one wad into the case,     -   introducing the projectile, in this case the shot,     -   crimping the case.

The introduction of the obturator is very easy as the outer diameter d_(EXT) of the obturator is smaller than the inner diameter d_(INT) of the case, as seen in FIG. 7A. Next, the other elements forming the cartridge, specifically the wad and projectile, are introduced in an entirely known manner before crimping, as seen in FIG. 7B. It will be observed that crimping, which consists of rolling the edges of the case on an operculum or folding the card into a star, which is also completely known, produces a reduction in the height of the case, which leads to initial pressure being applied to all the elements introduced into the cartridge and thus to the obturator, as seen in FIG. 7C.

Said pressure is limited but places the ribs 26 of the obturator in contact with the inner wall of the case 12.

The operation of the obturator 20 according to the present invention will now be described.

When the powder 18 is rapidly combusted and the explosion takes place in the region of the base 14, the role of the obturator 20 and the wad 22 is to transfer the energy generated by the explosion to the shot 24 to allow said shot to be projected. The mechanical behavior of the obturator is therefore fundamental to the firing quality.

It is therefore important that the join between the periphery of the circle formed by the upper circular edge 34 and the lower circular edge 36 is as airtight as possible relative to the inner wall of the case. As the excess pressure produced on the face of the obturator is on the side of the lower ribs 28 and on the lower face 20-1 of the disk 25, the obturator is subject to compression under the effect of the thrust generated by the explosion acting on said lower face of the disk 25 and on the lower ribs 28. The lower ribs 28 are therefore brought back to the plane of the disk.

At the same time, the upper ribs 27 are brought back to the plane of the disk by the movement of the obturator 20 which bears on the wad 22 topped by the shot 24, elements which are not yet subject to any action linked to the explosion in this phase, as seen in FIG. 7D. The lower ribs 28 meanwhile are compressed and rest against the upper ribs 27 immobilized against the wad. There is therefore a planar continuity between the ribs 26 and the disk 25. It will be noted with reference to FIGS. 6A and 6B that when flattened, as the theoretical diameter d_(EXT), shown by a dotted line, is greater than the inner diameter of the case d_(INT), the case which was constrained by the flattened obturator, deforms and is pressed against the cylinder, deforming said cylinder radially, said deformation being less than the theoretical deformation, until the outer wall of the case comes against the inner wall of the FC barrel. The inner wall of the FC barrel confines the outer wall of the case and thus the obturator radially and very significant radial pressure is produced from the recessed portion of the obturator.

The radial seal is extremely strong and at the same time leakages are negligible while the ballistic parameters are excellent.

In the central portion, because the radial rectilinear edges of the ribs with the linking membranes 38 thereof are staggered, the seal is reinforced even if one or more of the linking membranes 38 are torn as the deflector effect is totally dominant. During manufacture and post-manufacture handling, the linking membrane 38 may be partly or completely torn and therefore inoperative, but this does not degrade the seal performance and hence the ballistic values as the ribs 26 are pressed down by very significant pressure. Hence, almost all the thrust of the gases is transmitted to the obturator 20 which then bears on the wad 22, which distributes said thrust to the shot 24, and here too transmits almost all of said thrust.

The lower 28 and upper 27 ribs are therefore brought closer by the compression to which the obturator 20 is subject. The upper circular edges 34 and the lower peripheral edges 36 are also moved radially away from the disk 25 and are therefore pressed and rest against the inner wall of the case 12. Referring to FIGS. 6A and 6B, it will be observed that when flattened, as the theoretical diameter D_(EXT), shown as a dotted line, is greater than the inner diameter of the case d_(INT), the case in the cylinder of the FC barrel confining said case radially, very significant radial pressure is produced from the recessed portion of the obturator linked to the diametric differential. Said radial expansion compresses the circular edges 34 and 36 on the inner wall of the case 12, which is also pressed against the inner wall of the cylinder of the barrel. The peripheral seal is therefore provided and strengthened. The radial seal is extremely strong and leakages are negligible while the ballistic parameters are excellent.

From an environmental point of view, the material used to manufacture the obturator 20 may be biodegradable. At the moment of the explosion, the disk 25 and the upper ribs 27 are compressed on the wad 22, the lower ribs 28 are compressed on the upper ribs 27, the edges 34 and 36 are then compressed against the inner wall of the case 12, and the assembly, except for the membranes 38, is compressed but at no time stretched. The mechanical characteristics of biodegradable materials comply with the compression stresses applied to the obturator 20.

Biodegradable materials tend to change over time and lose plasticity for example or suffer dimensional variations. It will be observed that if, for example, the material becomes more brittle causing one or more ribs to break, the architecture allows the upper and lower ribs to be pressed together forming a continuous surface and compensating for said breakage. Similarly, if the diameter d_(EXT) changes, the ribs compensate in diameter and the reduction in radial pressure will be miniscule and quite sufficient to provide a suitable seal.

This is a very important element as biodegradable materials change owing to the presence of organic charges, natural, plant-based fibers or powders, plant-based polymers or those produced by microbiological techniques. Therefore, some degradation over time necessarily occurs, this being the primary appeal of said materials and what is sought after said obturators have been used and dispersed in nature.

The hunting season in particular is of limited duration and cartridge-type ammunition bought in one year may be kept for one or more years before being used. Different types of shot may be bought depending on the game and the different caliber guns even though all the ammunition bought during a year has not been used, not forgetting the normal stocks that remain at the end of the season. It is therefore imperative that cartridges using an obturator according to the present invention retain their ballistic performance at least from one year to the next or even over a period of years. The main user parameter is ballistic performance but while a user may be prepared to pay a higher price for cartridges with ecological properties, the same user will not tolerate a loss of ballistic performance.

The obturator according to the present invention is biodegradable, enables radial compensatory expansion and allows uniform, constant transmission of thrust to develop over time.

It will be understood that the internal architecture may vary in terms of wads, the arrangement of the obturator, for example between two wads, but the obturator remains the same, as does the operation thereof. Similarly, the nature of the wads may vary depending on the application and projectiles. However, this does not form part of the present invention. 

1. Shotgun cartridge comprising a case (12) of internal diameter d_(INT) and a base (14) with a primer (16), the powder (18), a wad (22) and the shot (24), as well as an obturator (20) arranged between the powder (18) and the wad (22), characterized in that the obturator (20) is made of biodegradable material with plastic deformation properties, and comprises a central disk (25) and ribs (26) together forming a one-piece element with the disk, the assembly having an outer diameter d_(EXT), the ribs (26) comprising upper ribs (27) and lower ribs (28), these ribs (26) forming a non-zero angle with the plane of the disk (25), the obturator having a nominal outer diameter d_(EXT), the ribs being able to take at least one other position in which said ribs (26) are in the plane of the disk (25), the outer diameter being D_(EXT).
 2. Shotgun cartridge according to claim 1, characterized in that the diameter D_(EXT) of the obturator (20) with the ribs in the plane of the disk (25) is greater than the inner diameter d_(INT) of the case.
 3. Shotgun cartridge according to claim 1, characterized in that the nominal outer diameter d_(EXT) of the obturator (20) is less than the inner diameter d_(INT) of the case (12).
 4. Shotgun cartridge according to claim 1, characterized in that the obturator comprises a linking membrane (38) between the ribs (26).
 5. Shotgun cartridge according to claim 1, characterized in that the obturator (20) comprises eight upper ribs (27) and eight lower ribs (28).
 6. Shotgun cartridge according to claim 1, characterized in that the upper ribs (27) and the lower ribs (28) comprise two radial rectilinear edges (30) and a circular edge (32) forming the periphery of the obturator (20) with an upper circular edge (34) and a lower circular edge (36).
 7. Shotgun cartridge according to claim 6, characterized in that the radial rectilinear edges (30) of the upper ribs (27) are staggered relative to the lower ribs (28).
 8. Shotgun cartridge according to claim 1, characterized in that the upper ribs (27) form an angle of more than 0° and in that the lower ribs (28) form an angle of less than 0°, with the plane of the central disk (25).
 9. Shotgun cartridge according to claim 8, characterized in that the upper ribs (27) form an angle of about 30° and in that the lower ribs (28) form an angle of about −30°, with the plane of the central disk (25).
 10. Method for producing a shotgun cartridge according to claim 1, characterized in that it comprises the following steps: preparing a base (14) with the case thereof (12), said base comprising a primer (16) and a powder charge (18), introducing an obturator (20) into the case (12), introducing at least one wad (22) into said case (12), introducing the projectile (24) into said case (12), crimping the case (12). 